Systems and methods for positron emission tomography image reconstruction

ABSTRACT

Methods and systems for PET image reconstruction are provided. A method may include obtaining an image sequence associated with a subject. The image sequence may include one or more images generated via scanning the subject at one or more consecutive time periods. The method may also include obtaining a target machine learning model. The method may further include generating at least one target image using the target machine learning model based on the image sequence. The at least one target image may present a dynamic parameter associated with the subject. The target machine learning model may provide a mapping between the image sequence and the at least one target image.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part application of U.S. patentapplication Ser. No. 17/321,628, filed on May 17, 2021, which is aContinuation of U.S. patent application Ser. No. 16/374,672 (issued asU.S. Pat. No. 11,010,938), filed on Apr. 3, 2019, the contents of whichis incorporated herein by reference.

TECHNICAL FIELD

This disclosure generally relates to Positron Emission Tomography (PET)technology, and more particularly, to methods and systems for imagereconstruction.

BACKGROUND

Positron Emission Tomography (PET) systems are widely used in medicaldiagnosis. Using a PET system, a biologically active molecule carrying aradioactive tracer is first introduced into a patient's body. The PETsystem then detects radiation (also referred to as PET scan data)emitted by the radioactive tracer and constructs an image of theradioactive tracer concentration within the body by analyzing detectedsignals. Because the biologically active molecules are naturalsubstrates of metabolism at a target organ or tissue, a parametric imagereconstructed based on the PET scan data, whose voxels or pixelspresenting a value of some physiological parameter (also referred to asdynamic parameter) of tracer kinetics, can aid the evaluation of thephysiology (functionality) and/or anatomy (structure) of the targetorgan or tissue, as well as its biochemical properties. At present, aparametric image may be reconstructed using an indirectionreconstruction algorithm (e.g., a Patlak model), a direct reconstructionalgorithm (e.g., a four-dimensional reconstruction model), etc. Usingthe indirection reconstruction algorithm, a portion of PET scan data maybe used to reconstruction an image frame, which may increase noises in areconstructed image, and decrease image quality. Using the directreconstruction algorithm, the four-dimensional reconstruction model iscomplex, which may need more iterations and decrease reconstructionspeed. Thus, it is desirable to provide systems and methods forreconstructing a parametric image with improved quality andreconstruction speed.

SUMMARY

In a first aspect of the present disclosure, a system for imagereconstruction is provided. The system may include at least one storagedevice and at least one processor. The at least one storage medium maystore executable instructions. The at least one processor may beconfigured to be in communication with the at least one storage device,wherein when executing the executable instructions, the system isconfigured to perform one or more of the following operations. Thesystem may obtain an image sequence associated with a subject. The imagesequence may include one or more images generated via scanning thesubject at one or more consecutive time periods. The system may obtain atarget machine learning model. The system may generate, based on theimage sequence, at least one target image using the target machinelearning model. The at least one target image may present a dynamicparameter associated with the subject. The target machine learning modelmay provide a mapping between the image sequence and the at least onetarget image.

In some embodiments, the system may input the image sequence associatedwith the subject into the target machine learning model. The system mayconvert the image sequence into the at least one target image.

In some embodiments, the system may obtain a plasma time activity curveassociated with the subject. The system may generate the at least onetarget image by inputting the image sequence and the plasma timeactivity curve associated with the subject into the target machinelearning model.

In some embodiments, the system may obtain, based on the image sequence,the plasma time activity curve associated with the subject using anadditional target machine learning model. The additional target machinelearning model may provide a mapping between the image sequence and theplasma time activity curve.

In some embodiments, a determination of the target machine learningmodel may include: obtaining multiple groups of training data associatedone or more samples, each group of the multiple groups of training dataincluding a first image sequence and a reference parametric imagecorresponding to the first image sequence, the reference parametricimage presenting the dynamic parameter associated with one of the one ormore samples; and generating the target machine learning model bytraining a machine learning model using the multiple groups of trainingdata.

In some embodiments, the system may, for each group of the multiplegroup of training data, obtain projection data associated with the oneof the one or more samples. The system may generate, based on theprojection data the first image sequence using a first imagereconstruction algorithm. The system may generate, based on theprojection data the first parametric image using a second imagereconstruction algorithm.

In some embodiments, the second image reconstruction algorithm mayinclude a four-dimensional (4D) iteration technique.

In some embodiments, the determination of the target machine learningmodel may further include: obtaining a reference plasma time activitycurve associated with the one of the one or more samples. The generatingthe target machine learning model by training the machine learning modelusing the multiple groups of training data may include: training, basedon the reference plasma time activity curve, the machine learning modelusing the multiple groups of training data.

In some embodiments, the reference plasma time activity curve associatedwith the one of the one or more samples may be determined based on theimage sequence associated with the one of the one or more samples.

In some embodiments, the determination of the target machine learningmodel may further include: obtaining multiple groups of validation data,each group of the multiple groups of validation data including a secondimage sequence and a second parametric image corresponding to the secondimage sequence, the second parametric image presenting the dynamicparameter; and adjusting the target machine learning model using themultiple groups of validation data.

In some embodiments, the target machine learning model may beconstructed based on a deep learning neural network model.

In some embodiments, the deep learning neural network model may includea convolution neural network (CNN) model.

In a second aspect of the present disclosure, a method for imagereconstruction is provided. The method may be implemented on a computingapparatus, the computing apparatus including at least one processor andat least one storage device. The method may include one or more of thefollowing operations. The method may include obtaining an image sequenceassociated with a subject. The image sequence may include one or moreimages generated via scanning the subject at one or more consecutivetime periods. The method may also include obtaining a target machinelearning model. The method may further include generating at least onetarget image using the target machine learning model based on the imagesequence. The at least one target image may present a dynamic parameterassociated with the subject. The target machine learning model mayprovide a mapping between the image sequence and the at least one targetimage.

In a third aspect of the present disclosure, a non-transitory computerreadable medium is provided. The non-transitory computer readable mediummay include at least one set of instructions that, when executed by atleast one processor, cause the at least one processor to effectuate amethod. The method may include one or more of the following operations.The at least one processor may obtain an image sequence associated witha subject. The image sequence may include one or more images generatedvia scanning the subject at one or more consecutive time periods. The atleast one processor may obtain a target machine learning model. The atleast one processor may generate, based on the image sequence, at leastone target image using the target machine learning model. The at leastone target image may present a dynamic parameter associated with thesubject. The target machine learning model may provide a mapping betweenthe image sequence and the at least one target image.

Additional features will be set forth in part in the description whichfollows, and in part will become apparent to those skilled in the artupon examination of the following and the accompanying drawings or maybe learned by production or operation of the examples. The features ofthe present disclosure may be realized and attained by practice or useof various aspects of the methodologies, instrumentalities, andcombinations set forth in the detailed examples discussed below.

BRIEF DESCRIPTION OF THE DRAWINGS

The present disclosure is further described in terms of exemplaryembodiments. These exemplary embodiments are described in detail withreference to the drawings. These embodiments are non-limiting exemplaryembodiments, in which like reference numerals represent similarstructures throughout the several views of the drawings, and wherein:

FIG. 1 is a schematic diagram illustrating an exemplary imaging systemaccording to some embodiments of the present disclosure;

FIG. 2 is a schematic diagram illustrating hardware and/or softwarecomponents of an exemplary computing device on which the processingdevice may be implemented according to some embodiments of the presentdisclosure;

FIG. 3 is a schematic diagram illustrating hardware and/or softwarecomponents of an exemplary mobile device according to some embodimentsof the present disclosure;

FIG. 4 is a block diagram illustrating an exemplary processing deviceaccording to some embodiments of the present disclosure;

FIG. 5 is a flowchart illustrating an exemplary process forreconstructing an image according to some embodiments of the presentdisclosure;

FIG. 6 is a flowchart illustrating an exemplary process forreconstructing an image according to some embodiments of the presentdisclosure;

FIG. 7 is a flowchart illustrating an exemplary process for training amachine learning model according to some embodiments of the presentdisclosure;

FIG. 8 is a flowchart illustrating an exemplary process for training amachine learning model according to some embodiments of the presentdisclosure;

FIG. 9 is a schematic diagram illustrating an exemplary convolutionalneural network (CNN) model according to some embodiments of the presentdisclosure;

FIG. 10 shows exemplary torsos images of three patients reconstructedaccording to some embodiments of the present disclosure;

FIG. 11 shows exemplary torsos images of three patients described inFIG. 10 reconstructed according to some embodiments of the presentdisclosure; and

FIG. 12 shows exemplary torsos images of three patients described inFIG. 10 reconstructed according to some embodiments of the presentdisclosure.

DETAILED DESCRIPTION

The following description is presented to enable any person skilled inthe art to make and use the present disclosure and is provided in thecontext of a particular application and its requirements. Variousmodifications to the disclosed embodiments will be readily apparent tothose skilled in the art, and the general principles defined herein maybe applied to other embodiments and applications without departing fromthe spirit and scope of the present disclosure. Thus, the presentdisclosure is not limited to the embodiments shown, but is to beaccorded the widest scope consistent with the claims.

It will be understood that the term “system,” “engine,” “unit,”“module,” and/or “block” used herein are one method to distinguishdifferent components, elements, parts, section or assembly of differentlevel in ascending order. However, the terms may be displaced by anotherexpression if they may achieve the same purpose.

Generally, the word “module,” “unit,” or “block,” as used herein, refersto logic embodied in hardware or firmware, or to a collection ofsoftware instructions. A module, a unit, or a block described herein maybe implemented as software and/or hardware and may be stored in any typeof non-transitory computer-readable medium or another storage device. Insome embodiments, a software module/unit/block may be compiled andlinked into an executable program. It will be appreciated that softwaremodules can be callable from other modules/units/blocks or fromthemselves, and/or may be invoked in response to detected events orinterrupts. Software modules/units/blocks configured for execution oncomputing devices (e.g., processor 210 as illustrated in FIG. 2 ) may beprovided on a computer-readable medium, such as a compact disc, adigital video disc, a flash drive, a magnetic disc, or any othertangible medium, or as a digital download (and can be originally storedin a compressed or installable format that needs installation,decompression, or decryption prior to execution). Such software code maybe stored, partially or fully, on a storage device of the executingcomputing device, for execution by the computing device. Softwareinstructions may be embedded in firmware, such as an ErasableProgrammable Read Only Memory (EPROM). It will be further appreciatedthat hardware modules/units/blocks may be included in connected logiccomponents, such as gates and flip-flops, and/or can be included ofprogrammable units, such as programmable gate arrays or processors. Themodules/units/blocks or computing device functionality described hereinmay be implemented as software modules/units/blocks, but may berepresented in hardware or firmware. In general, themodules/units/blocks described herein refer to logicalmodules/units/blocks that may be combined with othermodules/units/blocks or divided into sub-modules/sub-units/sub-blocksdespite their physical organization or storage. The description may beapplicable to a system, an engine, or a portion thereof.

The terminology used herein is for the purpose of describing particularexample embodiments only and is not intended to be limiting. As usedherein, the singular forms “a,” “an,” and “the” may be intended toinclude the plural forms as well, unless the context clearly indicatesotherwise. It will be further understood that the terms “comprise,”“comprises,” and/or “comprising,” “include,” “includes,” and/or“including,” when used in this specification, specify the presence ofstated features, integers, steps, operations, elements, and/orcomponents, but do not preclude the presence or addition of one or moreother features, integers, steps, operations, elements, components,and/or groups thereof.

These and other features, and characteristics of the present disclosure,as well as the methods of operation and functions of the relatedelements of structure and the combination of parts and economies ofmanufacture, may become more apparent upon consideration of thefollowing description with reference to the accompanying drawings, allof which form a part of this disclosure. It is to be expresslyunderstood, however, that the drawings are for the purpose ofillustration and description only and are not intended to limit thescope of the present disclosure. It is understood that the drawings arenot to scale.

The flowcharts used in the present disclosure illustrate operations thatsystems implement according to some embodiments in the presentdisclosure. It is to be expressly understood, the operations of theflowchart may be implemented not in order. Conversely, the operationsmay be implemented in inverted order, or simultaneously. Moreover, oneor more other operations may be added to the flowcharts. One or moreoperations may be removed from the flowcharts.

An aspect of the present disclosure relates to systems and methods fordetermining a parametric image in a PET imaging system. As used herein,the parametric image may include voxels or pixels whose value presentinga value of a physiological parameter (also referred to as dynamicparameter) of tracer kinetics. The parametric image may aid theevaluation of the physiology (functionality) and/or anatomy (structure)of the target organ or tissue, as well as its biochemical properties. Tothis end, a system may obtain an image sequence associated with asubject. The image sequence may include one or more images generated viascanning the subject at one or more consecutive time periods. The one ormore images may be one or more standardized uptake value (SUV) images.The system may obtain a target machine learning model. The targetmachine learning model may be obtained by training a machine learningmodel using a training set and a validation set. The target machinelearning model may provide a mapping relationship between the imagesequence and at least one corresponding parametric image. The system maygenerate, based on the image sequence, at least one parametric imageusing the target machine learning model. The at least one parametricimage may present a dynamic parameter associated with the subject. Usingthe target machine model for parametric image reconstruction, an imagesequence may be inputted the target machine model and a parametric imagemay be output, which may improve reconstruction speed. The targetmachine learning model may be trained for learning to analyze andextract information presented in the inputted data to generate aparametric image, which may improve quality of the generated parametricimage.

FIG. 1 is a schematic diagram illustrating an exemplary the imagingsystem 100 according to some embodiments of the present disclosure. Theimaging system 100 may be a single-modality system. Exemplarysingle-modality system may include a single-photon emission computedtomography (SPECT) system, a positron emission computed tomography (PET)system, etc. The imaging system 100 may also be a multi-modality system.Exemplary multi-modality systems may include a computedtomography-positron emission tomography (CT-PET) system, a magneticresonance-positron emission tomography (MR-PET) system, etc. In someembodiments, the multi-modality imaging system may include modulesand/or components for performing emission computed tomography imagingand/or related analysis.

For illustration purposes, as shown in FIG. 1 , the imaging system 100may include a scanner 110, a processing device 120, a storage device130, one or more terminals 140, and a network 150. The components in theimaging system 100 may be connected in one or more of various ways.Merely by way of example, the scanner 110 may be connected to theprocessing device 120 through the network 150. As another example, thescanner 110 may be connected to the processing device 120 directly. As afurther example, the terminal(s) 140 may be connected to anothercomponent of the imaging system 100 (e.g., the processing device 120)via the network 150 as illustrated in FIG. 1 . As still a furtherexample, the terminal(s) 140 may be connected to the processing device120 directly as illustrated by the dotted arrow in FIG. 1 . As still afurther example, the storage device 130 may be connected to anothercomponent of the imaging system 100 (e.g., the processing device 120)directly as illustrated in FIG. 1 , or through the network 150.

The scanner 110 may scan at least part of a subject, and/or generatedata relating to the subject. In some embodiments, the scanner 110 maybe an imaging device, for example, a PET device, a PET-CT device, aPET-MRI device, etc. In the present disclosure, “object” and “subject”are used interchangeably. The subject may be biological ornon-biological. For example, the subject may include a patient, aman-made object, etc. As another example, the subject may include aspecific portion, organ, and/or tissue of the patient. For example, thesubject may include the head, the brain, the neck, the body, a shoulder,an arm, the thorax, the heart, the stomach, a blood vessel, a softtissue, a knee, a foot, or the like, or a combination thereof, of thepatient.

The scanner 110 may include a gantry, a detector, an electronics module,a table, and/or other components not shown, for example a coolingassembly. The scanner 110 may scan a subject and obtain informationrelated with the subject. The gantry may support components (e.g., thedetector) necessary to produce and detect radiation events to generatean image. The table may position a subject in a detection region. Thedetector may detect radiation events (e.g., gamma photons) emitted fromthe detection region. In some embodiments, the detector may include aplurality of detector units. The detector units may be implemented in asuitable manner, for example, a ring, a rectangle, or an array. In someembodiments, the detector unit may include one or more crystal elementsand/or one or more photomultiplier tubes (PMT) (not shown). In someembodiments, a PMT as employed in the present disclosure may be asingle-channel PMT or a multi-channel PMT. The electronics module maycollect and/or process electrical signals (e.g., scintillation pulses)generated by the detector. The electronics module may include an adder,a multiplier, a subtracter, an amplifier, a drive circuit, adifferential circuit, a integral circuit, a counter, a filter, ananalog-to-digital converter (ADC), a lower limit detection (LLD)circuit, a constant fraction discriminator (CFD) circuit, atime-to-digital converter (TDC), a coincidence circuit, or the like, orany combination thereof. In some embodiments, the detected radiationevents may be stored or archived in a storage (e.g., the storage device130), displayed on a display (e.g., a screen on a computing device), ortransferred to a connected device (e.g., an external database). In someembodiments, a user may control the scanner 110 via a computing device.

The processing device 120 may process data and/or information obtainedfrom the scanner 110, the terminal(s) 140, and/or the storage device130. For example, the processing device 120 may obtain an image sequenceassociated with a subject. The image sequence including one or moreimages generated via scanning the subject at one or more time periods(e.g., one or more consecutive time periods, one or more non-consecutivetime periods) by the scanner 110. As another example, the processingdevice 120 may obtain a target machine learning model. The targetmachine learning model may provide a mapping between the image sequenceand at least one target image. As still an example, the processingdevice 120 may generate, based on the image sequence, the at least onetarget image using the target machine learning model. The at least onetarget image may present a dynamic parameter associated with thesubject. In some embodiments, the processing device 120 may obtain thetarget machine learning model by training a machine learning model usinga plurality of groups of training data (i.e., training set). The targetmachine learning model may be updated from time to time, e.g.,periodically or not, based on training data that is at least partiallydifferent from the original training set from which the target machinelearning model is determined. For instance, the target machine learningmodel may be updated based on a training set including new training datathat are not in the original training set. In some embodiments, thedetermination and/or updating of the target machine learning model maybe performed on a processing device, while the application of the targetmachine learning model may be performed on a different processingdevice. In some embodiments, the determination and/or updating of thetarget machine learning model may be performed on a processing device ofa system different than the imaging system 100 on which the applicationof the target machine learning model is performed. For instance, thedetermination and/or updating of the target machine learning model maybe performed on a first system of a vendor who provides and/or maintainssuch a machine learning model and/or has access to training samples usedto determine and/or update the target machine learning model, while theapplication of the provided machine learning model, may be performed ona second system of a client of the vendor. In some embodiments, thedetermination and/or updating of the target machine learning model maybe performed online in response to a request for image reconstruction.In some embodiments, the determination and/or updating of the targetmachine learning model may be performed offline. In some embodiments, areconstructed image may be transmitted to the terminal(s) 140 anddisplayed on one or more display devices in the terminal(s) 140. In someembodiments, the processing device 120 may be a single server or aserver group. The server group may be centralized or distributed. Insome embodiments, the processing device 120 may be local or remote. Forexample, the processing device 120 may access information and/or datastored in the scanner 110, the terminal(s) 140, and/or the storagedevice 130 via the network 150. As another example, the processingdevice 120 may be directly connected to the scanner 110, the terminal(s)140 and/or the storage device 130 to access stored information and/ordata. In some embodiments, the processing device 120 may be implementedon a cloud platform. Merely by way of example, the cloud platform mayinclude a private cloud, a public cloud, a hybrid cloud, a communitycloud, a distributed cloud, an inter-cloud, a multi-cloud, or the like,or any combination thereof. In some embodiments, the processing device120 may be implemented by a computing device 200 having one or morecomponents as illustrated in FIG. 2 .

The storage device 130 may store data, instructions, and/or any otherinformation. In some embodiments, the storage device 130 may store dataobtained from the terminal(s) 140 and/or the processing device 120. Forexample, the storage device 130 may store PET scan data obtained fromthe scanner 110. As another example, the storage device 130 may store atarget machine learning model as described elsewhere in the presentdisclosure (e.g., FIG. 7 and the descriptions thereof). In someembodiments, the storage device 130 may store data and/or instructionsthat the processing device 120 may execute or use to perform exemplarymethods described in the present disclosure. In some embodiments, thestorage device 130 may include a mass storage, removable storage, avolatile read-and-write memory, a read-only memory (ROM), or the like,or any combination thereof. Exemplary mass storage may include amagnetic disk, an optical disk, a solid-state drive, etc. Exemplaryremovable storage may include a flash drive, a floppy disk, an opticaldisk, a memory card, a zip disk, a magnetic tape, etc. Exemplaryvolatile read-and-write memory may include a random access memory (RAM).Exemplary RAM may include a dynamic RAM (DRAM), a double date ratesynchronous dynamic RAM (DDR SDRAM), a static RAM (SRAM), a thyristorRAM (T-RAM), and a zero-capacitor RAM (Z-RAM), etc. Exemplary ROM mayinclude a mask ROM (MROM), a programmable ROM (PROM), an erasableprogrammable ROM (EPROM), an electrically erasable programmable ROM(EEPROM), a compact disk ROM (CD-ROM), and a digital versatile disk ROM,etc. In some embodiments, the storage device 130 may be implemented on acloud platform. Merely by way of example, the cloud platform may includea private cloud, a public cloud, a hybrid cloud, a community cloud, adistributed cloud, an inter-cloud, a multi-cloud, or the like, or anycombination thereof.

In some embodiments, the storage device 130 may be connected to thenetwork 150 to communicate with one or more other components of theimaging system 100 (e.g., the processing device 120, the terminal(s)140). One or more components of the imaging system 100 may access thedata or instructions stored in the storage device 130 via the network150. In some embodiments, the storage device 130 may be directlyconnected to or communicate with one or more other components of theimaging system 100 (e.g., the processing device 120, the terminal(s)140). In some embodiments, the storage device 130 may be part of theprocessing device 120.

The terminal(s) 140 may include a mobile device 140-1, a tablet computer140-2, a laptop computer 140-3, or the like, or any combination thereof.In some embodiments, the mobile device 140-1 may include a smart homedevice, a wearable device, a mobile device, a virtual reality device, anaugmented reality device, or the like, or any combination thereof.Merely by way of example, the terminal(s) 140 may include a mobiledevice as illustrated in FIG. 3 . In some embodiments, the smart homedevice may include a smart lighting device, a control device of anintelligent electrical apparatus, a smart monitoring device, a smarttelevision, a smart video camera, an interphone, or the like, or anycombination thereof. In some embodiments, the wearable device mayinclude a bracelet, footwear, eyeglasses, a helmet, a watch, clothing, abackpack, a smart accessory, or the like, or any combination thereof. Insome embodiments, the mobile device may include a mobile phone, apersonal digital assistant (PDA), a gaming device, a navigation device,a point of sale (POS) device, a laptop, a tablet computer, a desktop, orthe like, or any combination thereof. In some embodiments, the virtualreality device and/or the augmented reality device may include a virtualreality helmet, virtual reality glasses, a virtual reality patch, anaugmented reality helmet, augmented reality glasses, an augmentedreality patch, or the like, or any combination thereof. For example, thevirtual reality device and/or the augmented reality device may include aGoogle Glass™, an Oculus Rift™, a Hololens™, a Gear VR™, etc. In someembodiments, the terminal(s) 140 may be part of the processing device120.

In some embodiments, the terminal(s) 140 may send and/or receiveinformation for parametric image reconstruction to the processing device120 via a user interface. The user interface may be in the form of anapplication for parametric image reconstruction implemented on theterminal(s) 140. The user interface implemented on the terminal(s) 140may be configured to facilitate communication between a user and theprocessing device 120. In some embodiments, a user may input a requestfor parametric image reconstruction via the user interface implementedon the terminal(s) 140. The terminal(s) 140 may send the request forparametric image reconstruction to the processing device 120 forreconstructing a parametric image based on a target machine learningmodel as described elsewhere in the present disclosure (e.g., FIG. 5 andthe descriptions thereof). In some embodiments, the user may inputand/or adjust parameters (e.g., weights) of the target machine learningmodel via the user interface. In some embodiments, the user interfacemay facilitate the presentation or display of information and/or data(e.g., a signal) relating to parametric image reconstruction receivedfrom the processing device 120. For example, the information and/or datamay include a result generated by the processing device 120 in an imagereconstruction. For example, the result may include one or more images(e.g., 2D images, 3D images, etc.), one or more data figures, one ormore words, one or more digits, one or more models for parametric imagereconstruction, parameters used in such image reconstruction, etc. Insome embodiments, the information and/or data may be further configuredto cause the terminal(s) 140 to display the result to the user.

The network 150 may include any suitable network that can facilitate theexchange of information and/or data for the imaging system 100. In someembodiments, one or more components of the imaging system 100 (e.g., thescanner 110, the terminal(s) 140, the processing device 120, the storagedevice 130, etc.) may communicate information and/or data with one ormore other components of the imaging system 100 via the network 150. Forexample, the processing device 120 may obtain image data from thescanner 110 via the network 150. As another example, the processingdevice 120 may obtain user instructions from terminal(s) 140 via thenetwork 150. The network 150 may be and/or include a public network(e.g., the Internet), a private network (e.g., a local area network(LAN), a wide area network (WAN))), a wired network (e.g., an Ethernetnetwork), a wireless network (e.g., an 802.11 network, a Wi-Fi network),a cellular network (e.g., a Long Term Evolution (LTE) network), a framerelay network, a virtual private network (“VPN”), a satellite network, atelephone network, routers, hubs, switches, server computers, and/or anycombination thereof. Merely by way of example, the network 150 mayinclude a cable network, a wireline network, a fiber-optic network, atelecommunications network, an intranet, a wireless local area network(WLAN), a metropolitan area network (MAN), a public telephone switchednetwork (PSTN), a Bluetooth™ network, a ZigBee™ network, a near fieldcommunication (NFC) network, or the like, or any combination thereof. Insome embodiments, the network 150 may include one or more network accesspoints. For example, the network 150 may include wired and/or wirelessnetwork access points such as base stations and/or internet exchangepoints through which one or more components of the imaging system 100may be connected to the network 150 to exchange data and/or information.

The network 150 may include any suitable network that can facilitate theexchange of information and/or data for the imaging system 100. In someembodiments, one or more components of the imaging system 100 (e.g., thescanner 110, the terminal(s) 140, the processing device 120, the storagedevice 130, etc.) may transmit or receive information and/or data withone or more other components of the imaging system 100 via the network150. For example, the processing device 120 may obtain image data fromthe scanner 110 via the network 150. As another example, the processingdevice 120 may obtain user instructions from the terminal(s) 140 via thenetwork 150. The network 150 may be and/or include a public network(e.g., the Internet), a private network (e.g., a local area network(LAN), a wide area network (WAN)), etc.), a wired network (e.g., anEthernet network), a wireless network (e.g., an 802.11 network, a Wi-Finetwork, etc.), a cellular network (e.g., a Long Term Evolution (LTE)network), a frame relay network, a virtual private network (“VPN”), asatellite network, a telephone network, routers, hubs, switches, servercomputers, and/or any combination thereof. Merely by way of example, thenetwork 150 may include a cable network, a wireline network, afiber-optic network, a telecommunications network, an intranet, awireless local area network (WLAN), a metropolitan area network (MAN), apublic telephone switched network (PSTN), a Bluetooth™ network, aZigBee™ network, a near field communication (NFC) network, or the like,or any combination thereof. In some embodiments, the network 150 mayinclude one or more network access points. For example, the network 150may include wired and/or wireless network access points such as basestations and/or internet exchange points through which one or morecomponents of the imaging system 100 may be connected with the network150 to exchange data and/or information.

FIG. 2 is a schematic diagram illustrating hardware and/or softwarecomponents of an exemplary computing device 200 on which the processingdevice 120 may be implemented according to some embodiments of thepresent disclosure. As illustrated in FIG. 2 , the computing device 200may include a processor 210, storage 220, an input/output (I/O) 230, anda communication port 240.

The processor 210 may execute computer instructions (program code) andperform functions of the processing device 120 in accordance withtechniques described herein. The computer instructions may include, forexample, routines, programs, objects, components, signals, datastructures, procedures, modules, and functions, which perform particularfunctions described herein. For example, the processor 210 may processdata obtained from the scanner 110, the terminal(s) 140, the storagedevice 130, and/or any other component of the imaging system 100.Specifically, the processor 210 may process one or more measured datasets (e.g., PET scan data) obtained from the scanner 110. For example,the processor 210 may reconstruct an image based on the data set(s). Insome embodiments, the reconstructed image may be stored in the storagedevice 130, the storage 220, etc. In some embodiments, the reconstructedimage may be displayed on a display device by the I/O 230. In someembodiments, the processor 210 may perform instructions obtained fromthe terminal(s) 140. In some embodiments, the processor 210 may includeone or more hardware processors, such as a microcontroller, amicroprocessor, a reduced instruction set computer (RISC), anapplication specific integrated circuits (ASICs), anapplication-specific instruction-set processor (ASIP), a centralprocessing unit (CPU), a graphics processing unit (GPU), a physicsprocessing unit (PPU), a microcontroller unit, a digital signalprocessor (DSP), a field programmable gate array (FPGA), an advancedRISC machine (ARM), a programmable logic device (PLD), any circuit orprocessor capable of executing one or more functions, or the like, orany combinations thereof.

Merely for illustration, only one processor is described in thecomputing device 200. However, it should be noted that the computingdevice 200 in the present disclosure may also include multipleprocessors. Thus operations and/or method steps that are performed byone processor as described in the present disclosure may also be jointlyor separately performed by the multiple processors. For example, if inthe present disclosure the processor of the computing device 200executes both operation A and operation B, it should be understood thatoperation A and operation B may also be performed by two or moredifferent processors jointly or separately in the computing device 200(e.g., a first processor executes operation A and a second processorexecutes operation B, or the first and second processors jointly executeoperations A and B).

The storage 220 may store data/information obtained from the scanner110, the terminal(s) 140, the storage device 130, or any other componentof the imaging system 100. In some embodiments, the storage 220 mayinclude a mass storage device, a removable storage device, a volatileread-and-write memory, a read-only memory (ROM), or the like, or anycombination thereof. For example, the mass storage may include amagnetic disk, an optical disk, a solid-state drive, etc. The removablestorage may include a flash drive, a floppy disk, an optical disk, amemory card, a zip disk, a magnetic tape, etc. The volatileread-and-write memory may include a random access memory (RAM). The RAMmay include a dynamic RAM (DRAM), a double date rate synchronous dynamicRAM (DDR SDRAM), a static RAM (SRAM), a thyristor RAM (T-RAM), and azero-capacitor RAM (Z-RAM), etc. The ROM may include a mask ROM (MROM),a programmable ROM (PROM), an erasable programmable ROM (PEROM), anelectrically erasable programmable ROM (EEPROM), a compact disk ROM(CD-ROM), and a digital versatile disk ROM, etc. In some embodiments,the storage 220 may store one or more programs and/or instructions toperform exemplary methods described in the present disclosure. Forexample, the storage 220 may store a program for the processing device120 for reconstructing a dynamic parameter image.

The I/O 230 may input or output signals, data, and/or information. Insome embodiments, the I/O 230 may enable user interaction with theprocessing device 120. In some embodiments, the I/O 230 may include aninput device and an output device. Exemplary input devices may include akeyboard, a mouse, a touch screen, a microphone, or the like, or acombination thereof. Exemplary output devices may include a displaydevice, a loudspeaker, a printer, a projector, or the like, or acombination thereof. Exemplary display devices may include a liquidcrystal display (LCD), a light-emitting diode (LED)-based display, aflat panel display, a curved screen, a television device, a cathode raytube (CRT), or the like, or a combination thereof.

The communication port 240 may be connected with a network (e.g., thenetwork 150) to facilitate data communications. The communication port240 may establish connections between the processing device 120 and thescanner 110, the terminal(s) 140, or the storage device 130. Theconnection may be a wired connection, a wireless connection, or acombination of both that enables data transmission and reception. Thewired connection may include an electrical cable, an optical cable, atelephone wire, or the like, or any combination thereof. The wirelessconnection may include Bluetooth, Wi-Fi, WiMax, WLAN, ZigBee, mobilenetwork (e.g., 3G, 4G, 5G, etc.), or the like, or a combination thereof.In some embodiments, the communication port 240 may be a standardizedcommunication port, such as RS232, RS485, etc. In some embodiments, thecommunication port 240 may be a specially designed communication port.For example, the communication port 240 may be designed in accordancewith the digital imaging and communications in medicine (DICOM)protocol.

FIG. 3 is a schematic diagram illustrating hardware and/or softwarecomponents of an exemplary mobile device 300 according to someembodiments of the present disclosure. As illustrated in FIG. 3 , themobile device 300 may include a communication platform 310, a display320, a graphics processing unit (GPU) 330, a central processing unit(CPU) 340, an I/O 350, a memory 370, and storage 390. In someembodiments, any other suitable component, including but not limited toa system bus or a controller (not shown), may also be included in themobile device 300. In some embodiments, a mobile operating system 360(e.g., iOS, Android, Windows Phone, etc.) and one or more applications380 may be loaded into the memory 370 from the storage 390 in order tobe executed by the CPU 340. The applications 380 may include a browseror any other suitable mobile apps for receiving and renderinginformation relating to image processing or other information from theprocessing device 120. User interactions with the information stream maybe achieved via the I/O 350 and provided to the processing device 120and/or other components of the imaging system 100 via the network 150.

To implement various modules, units, and their functionalities describedin the present disclosure, computer hardware platforms may be used asthe hardware platform(s) for one or more of the elements describedherein. The hardware elements, operating systems and programminglanguages of such computers are conventional in nature, and it ispresumed that those skilled in the art are adequately familiar therewithto adapt those technologies to generate an image as described herein. Acomputer with user interface elements may be used to implement apersonal computer (PC) or another type of work station or terminaldevice, although a computer may also act as a server if appropriatelyprogrammed. It is believed that those skilled in the art are familiarwith the structure, programming and general operation of such computerequipment and as a result, the drawings should be self-explanatory.

FIG. 4 is a block diagram illustrating an exemplary processing device120 according to some embodiments of the present disclosure. Theprocessing device 120 may include an acquisition module 402, a modeldetermination module 404, an image reconstruction module 406, and astorage module 408. At least a portion of the processing device 120 maybe implemented on a computing device as illustrated in FIG. 2 or amobile device as illustrated in FIG. 3 .

The acquisition module 402 may obtain an image sequence associated witha subject. The acquisition module 402 may obtain the image sequence fromthe scanner 110, the processing device 120, one or more storage devicesdisclosed in the present disclosure (e.g., the storage device 130), etc.In some embodiments, the image sequence may include one or more images.An image in the image sequence may be a PET image with voxels or pixelspresenting standardized uptake value (SUV) of a tracer (also referred toas SUV image). In some embodiments, the one or more images may bereconstructed independently using PET scan data acquired during each ofone or more time periods (e.g., one or more consecutive time periods,one or more non-consecutive time periods). In some embodiments, the oneor more images may be reconstructed dependently using PET scan dataacquired during the one or more consecutive time periods. In someembodiments, the one or more images may be reconstructed dependentlyusing PET scan data acquired during the one or more non-consecutive timeperiods.

In some embodiments, the acquisition model 402 may obtain a plasma timeactivity curve (TAC) associated with the subject. The plasma TAC may bedenoted by a function that the concentration of radioactivity of thetracer in the plasma changes with time. In some embodiments, theacquisition model 402 may determine the plasma TAC of the subject usinga golden standard technique, an arterialization of venous bloodtechnique, a PET blood pool scan technique, a standard input functiontechnique, a fitting function technique, or the like, or a combinationthereof, as described elsewhere in the present disclosure.

In some embodiments, the acquisition module 402 may send the imagesequence and/or the plasma TAC to other modules and/or units of theprocessing device 120 for further processing. For example, the imagesequence may be sent to the storage module 408 for storage. For anotherexample, the acquisition module 402 may send the image sequence and/orthe plasma TAC to the image reconstruction module 406 for reconstructingan image. In some embodiments, the acquisition module 402 may obtain oneor more machine learning models. For example, the acquisition module 402may obtain a target machine learning model configured to, for example,generate at least one target image presenting a dynamic parameter basedon the image sequence.

The model determination module 404 may determine one or more machinelearning models. For example, the model determination module 404 maydetermine a target machine learning model configured to, for example,generate at least one target image presenting a dynamic parameter basedon the image sequence obtained by the acquisition module 402. The targetmachine learning model may map a specific image sequence associated witha specific subject to a specific target image presenting a dynamicparameter associated with the specific subject. In some embodiments, thetarget machine learning model may be configured to map the specificimage sequence to the specific target image based on a specific plasmaTAC associated with the specific subject. For example, the targetmachine learning model may provide a mapping relationship between aspecific image sequence, a specific plasma TAC, and a specific targetimage presenting a dynamic parameter associated with a specific subject.

In some embodiments, the model determination module 404 may transmit adetermined target machine learning model to one or more other modulesfor further processing or application. For example, the modeldetermination module 404 may transmit a target machine learning model tothe storage module 408 for storage. As another example, the modeldetermination module 404 may transmit a target machine learning model tothe image reconstruction module 406 for image processing.

The image reconstruction module 406 may process information provided byvarious modules of the processing device 120. The image reconstructionmodule 406 may process an image sequence acquired by the acquisitionmodule 402, an image sequence retrieved from the storage module 408,etc. In some embodiments, the image reconstruction module 406 mayreconstruct a target image based on the image sequence according to areconstruction technique, generate a report including one or more imagesand/or other related information, and/or perform any other function forimage reconstruction in accordance with various embodiments of thepresent disclosure.

The image reconstruction module 406 may generate at least one targetimage based on the image sequence obtained by the acquisition module 402and a target machine learning model determined by the modeldetermination module 404. For example, the image sequence may beinputted into the target machine learning model. The at least one targetimage may be generated by the target machine learning model based on theinputted image sequence. In some embodiments, the image reconstructionmodule 406 may also reconstruct the at least one target image based onthe plasma TAC. For example, the plasma TAC and the image sequence maybe inputted into the target machine learning model. The target machinelearning model may convert the image sequence into the at least onetarget image based on the specific plasma TAC.

The storage module 408 may store information. The information mayinclude programs, software, algorithms, machine learning models, imagedata, control parameters, processed image data, or the like, or acombination thereof. For example, the information may include an imagesequence, at least one target image, a plasma TAC, a target machinelearning model, etc. In some embodiments, the storage module 408 maystore one or more programs and/or instructions that may be executed bythe processor(s) of the processing device 120 to perform exemplarymethods described in this disclosure. For example, the storage module408 may store program(s) and/or instruction(s) that can be executed bythe processor(s) of the processing device 120 to acquire image data,reconstruct an image based on the image data, train a machine learningmodel, and/or display any intermediate result or a resultant image.

In some embodiments, one or more modules illustrated in FIG. 4 may beimplemented in at least part of the exemplary imaging system 100 asillustrated in FIG. 1 . For example, the acquisition module 402, thestorage module 408, the model determination module 404, and/or the imagereconstruction module 406 may be integrated into a console (not shown).Via the console, a user may set parameters for scanning a subject,controlling imaging processes, controlling parameters for reconstructionof an image, viewing reconstructed images, etc. In some embodiments, theconsole may be implemented via the processing device 120 and/or theterminal(s) 140. In some embodiments, the model determination module 404may be integrated into the terminal(s) 140.

In some embodiments, the processing device 120 does not include themodel determination module 404. One or more target machine learningmodels determined by another device may be stored in the imaging system100 (e.g., the storage device 130, the storage 220, the storage 390, thememory 370, the storage module 408, etc.) or in an external deviceaccessible by the processing device 120 via, for example, the network150. In some embodiments, such a device may include a portion the sameas or similar to the model determination module 404. In someembodiments, the model determination module 404 may store one or moretarget machine learning models determined by another device and beaccessible by one or more components of the imaging system 100 (e.g.,the image reconstruction module 406, etc.). In some embodiments, atarget machine learning model applicable in the present disclosure maybe determined by the imaging system 100 (or a portion thereof including,e.g., the processing device 120) or an external device accessible by theimaging system 100 (or a portion thereof including, e.g., the processingdevice 120) following the processes disclosure herein.

FIG. 5 is a flowchart illustrating an exemplary process 500 forreconstructing an image according to some embodiments of the presentdisclosure. In some embodiments, one or more operations of process 500illustrated in FIG. 5 may be implemented in the imaging system 100illustrated in FIG. 1 . For example, process 500 illustrated in FIG. 5may be stored in the storage device 130 in the form of instructions, andinvoked and/or executed by the processing device 120 (e.g., theprocessor 210 of the computing device 200 as illustrated in FIG. 2 , theGPU 330 or CPU 340 of the mobile device 300 as illustrated in FIG. 3 ).

In 502, an image sequence associated with a subject may be obtained, theimage sequence including one or more images generated via scanning thesubject at one or more time periods. In some embodiments, the one ormore time periods are consecutive. For example, the image sequenceincluding one or more images may be generated via scanning the subjectwithin a consecutive five minutes (e.g., from 10:00 a.m. to 10:05 a.m.on one day). In some embodiments, the one or more time periods arenon-consecutive. For example, the image sequence including one or moreimages may be generated via scanning the subject within anon-consecutive five minutes. For example, some of the one or moreimages of the image sequence may be generated via scanning the subjectfrom 10:00 a.m. to 10:02 a.m. on one day, and remaining images of theone or more images of the image sequence may be generated via scanningthe subject from 11:00 a.m. to 11:03 a.m. on the day. Operation 502 maybe performed by the acquisition module 402. In some embodiments, theimage sequence may be obtained from the scanner 110, the processingdevice 120, one or more storage devices disclosed in the presentdisclosure (e.g., the storage device 130), etc. The one or more imagesin the image sequence may be also referred to as dynamic activity imagesof the subject, which may present a dynamic change of uptake of a tracer(or radioactive tracer) in one or more ROIs of the subject (e.g., atumor) with time. An image in the image sequence may be a standardizeduptake value (SUV) image with voxels or pixels presenting SUV associatedwith one or more regions of interests (ROIs) of the subject. A SUVassociated with an ROI may represent an uptake of a tracer (orradioactive tracer) of the ROI in the subject (e.g., a tumor) that isnormalized by an injected dose of the tracer and a body mass (or bodysurface area) of the subject. A SUV associated with an ROI may be usedto characterize the ROI. For example, if the SUV of the ROI is greaterthan a threshold, the ROI may be identified and/or determined as atumor.

In some embodiments, the one or more images in the image sequence may bereconstructed independently using PET scan data acquired during each ofthe one or more time periods (e.g., one or more consecutive timeperiods, one or more non-consecutive time periods). A specific SUV imagecorresponding to a specific time period may be reconstructed based onPET scan data acquired during a specific time period using an imagereconstruction algorithm. Exemplary image reconstruction algorithms mayinclude an iterative algorithm, an analysis algorithm, etc. Theiterative algorithm may include a Maximum Likelihood Estimation Method(MLEM) algorithm, an ordered subset expectation maximization (OSEM), a3D reconstruction algorithm, etc. The analysis algorithm may include afiltered back projection (FBP) algorithm. The PET scan data associatedwith the specific image may be obtained by a PET scanner (e.g., thescanner 110) by way of scanning the subject (e.g., a substance, anorgan, a tissue, etc.) during the specific time period. Typically, thePET scan data may include raw data (e.g., coincidence events) collectedduring the PET scanning, projection data, etc. The projection data maybe generated by processing the raw data by a processing device (e.g.,the processing device 120). The projection data may be stored as asinogram via a histogram-mode acquisition, or stored as a list mode filevia a list-mode acquisition.

In some embodiments, each of the one or more images in the imagesequence may be reconstructed using all PET scan data acquired duringthe one or more time periods (e.g., one or more consecutive timeperiods, one or more non-consecutive time periods). The one or moreimages may be reconstructed using, for example, an iterative temporalsmoothing model, an advanced temporal basis function, a principalcomponents transformation of dynamic data, a wavelet-based model, or thelike, or any combination.

As used herein, the one or more time periods (e.g., one or moreconsecutive time periods, one or more non-consecutive time periods) mayrefer to time periods after a time interval after the injection of atracer. The time interval may be set by a user or according to a defaultsetting of the imaging system 100, or may be adjustable under differentsituations. For example, the time interval may be 30 min, 40 min, etc.The time length of each of the one or more time periods (e.g., one ormore consecutive time periods, one or more non-consecutive time periods)may be set by a user or according to a default setting of the imagingsystem 100, or may be adjustable under different situations. Forexample, the time length may be 10 min, 20 min, or the like, or anycombination thereof. Taking a time interval as 30 min and a time lengthas 10 as an example, the first consecutive time period may be 30-40 minafter the injection of the tracer, and the second consecutive timeperiod may be 40-50 min after the injection of the tracer. During eachconsecutive time period, an image (i.e., a dynamic frame) may beacquired by the scanner 110 scanning the subject.

In 504, a target machine learning model may be obtained. Operation 504may be performed by the model determination module 404. The targetmachine learning model may be configured to use a specific imagesequence (e.g., the image sequence obtained in 502) as an input andgenerate a specific parametric image as an output. In some embodiments,the target machine learning model may be configured to provide a mappingrelationship between a specific image sequence and a specific targetimage presenting a dynamic parameter associated with a specific subject.As used herein, an image presenting a dynamic parameter associated witha subject may be also referred to as a parametric image. In other words,the target machine learning model may be used to convert the specificimage sequence associated with a specific subject into a specificparametric image based on the mapping relationship. For example, theimage sequence obtained in 502 may be inputted to the target machinelearning model. At least one target image presenting a dynamic parameterassociated with the subject may be generated by the target machinelearning model based on the inputted image sequence obtained in 502.

In some embodiments, the target machine learning model may be configuredto map the specific image sequence to the specific parametric imagebased on a specific plasma time activity curve (TAC) associated with thespecific subject. For example, the target machine learning model may beconfigured to provide a mapping relationship between a specific imagesequence, a specific plasma time activity curve (TAC), and a specifictarget image presenting a dynamic parameter (i.e., parametric image)associated with a specific subject. The specific plasma TAC associatedwith the specific subject and the specific image sequence may beinputted into the target machine learning model. The target machinelearning model may convert the specific image sequence into the specificparametric image of the specific subject based on the specific plasmaTAC. For another example, the target machine learning model may providea mapping relationship between the specific image sequence and thespecific plasma TAC. The specific image sequence may be inputted intothe target machine learning model. The target machine learning model maybe used to determine the specific plasma TAC of the specific subjectbased on the inputted specific image sequence. Further, the targetmachine learning model may provide a mapping relationship between thespecific image sequence, the determined specific plasma TAC, and thecorresponding specific parametric image of the specific subject.Detailed descriptions regarding the plasma TACs may be found elsewherein the present disclosure (e.g., FIG. 6 and the descriptions thereof).

The target machine learning model may be obtained from the modeldetermination module 404, the storage device 130, or any other storagedevice. For example, the model determination module 404 may generate thetarget machine learning model by training a machine learning model basedon multiple groups of training data using a model training algorithm.Exemplary model training algorithms may include a gradient descentalgorithm, a Newton's algorithm, a Quasi-Newton algorithm, aLevenberg-Marquardt algorithm, a conjugate gradient algorithm, or thelike, or a combination thereof. The multiple groups of training data(also referred to as training set) may be associated with one or moresamples same as or different from the subject as descried in 502. Eachof the multiple groups of training data may include an image sequenceand a reference parametric image of a specific sample. The imagesequence and the reference parametric image of the specific sample maybe reconstructed based on same PET scan data using differentreconstruction algorithms. In some embodiments, each group of themultiple groups of training data may include a corresponding plasma TACassociated with one of the one or more samples. More descriptions of thedetermination of the plasma TAC may be found elsewhere in the presentdisclosure (e.g., FIG. 6 and the descriptions thereof). Moredescriptions for the multiple groups of training data may be foundelsewhere in the present disclosure (e.g., FIG. 7 and the descriptionsthereof).

The machine learning model may be constructed based on a deep learningneural network model. Exemplary deep learning neural network models mayinclude a convolutional machine learning model (CNN), a fullyconvolutional neural network (FCN) model, a generative adversarialnetwork (GAN), a back propagation (BP) machine learning model, a radialbasis function (RBF) machine learning model, a deep belief nets (DBN),an Elman machine learning model, or the like, or a combination thereof.

In some embodiments, the machine learning model may be constructed basedon one single machine learning model. The one single machine learningmodel may be trained to provide the mapping relationship between thespecific image sequence, the specific plasma TAC, and the correspondingspecific parametric image of the specific subject, or the mappingrelationship between the specific image sequence and the correspondingspecific parametric image of the specific subject. In some embodiments,the one single trained machine learning model (i.e., the target machinelearning model) may be configured to convert an inputted specific imagesequence into a specific parametric image of a specific subject based onthe mapping relationship. In some embodiments, the one single trainedmachine learning model (i.e., the target machine learning model) may beconfigured to convert an inputted specific image sequence into aspecific parametric image of a specific subject based on the mappingrelationship and an inputted specific plasma TAC.

In some embodiments, the machine learning model may be constructed basedon at least two sub-models, e.g., a first sub-model and a secondsub-model. The first sub-model may be trained to provide the mappingrelationship between the specific image sequence and the specific plasmaTAC of the specific subject. The trained first sub-model may beconfigured to convert an inputted specific image sequence into aspecific plasma TAC of a specific subject. The second sub-model may betrained to provide the mapping relationship between the specific imagesequence, the determined specific plasma TAC and the correspondingspecific parametric image of the specific subject. The trained secondsub-model may be configured to convert the inputted specific imagesequence into a specific parametric image of a specific subject based onthe mapping relationship and the determined specific plasma TAC. In someembodiments, the first sub-model and the second sub-model may beindependent from each other. The training of the first sub-model and thesecond sub-model may be independent. In some embodiments, the firstsub-model and the second sub-model may be connected with each other via,for example, a node, a layer, etc. The first sub-model and the secondsub-model may be trained as a whole to determine the target machinelearning model.

During a training process of the machine learning model, the mappingrelationship between an image sequence and corresponding at least onetarget image may be established based on the multiple groups of trainingdata. In some embodiments, the trained machine learning model may bedetermined as the target machine learning model. In some embodiments,the trained machine learning model may be adjusted and/or optimizedusing one or more groups of validation data. The trained machinelearning model after being adjusted and/or optimized may be designatedas the target machine learning model. The target machine learning modelmay be generated according to the exemplary process for training amachine learning model disclosed elsewhere in the present disclosure(e.g., FIGS. 7-8 , the process 700 and the process 800).

In 506, at least one target image may be generated using the targetmachine learning model, the at least one target image presenting adynamic parameter associated with the subject. Operation 506 may beperformed by the image reconstruction module 406. In the at least onetarget image, each voxel or pixel may present a value of a dynamicparameter (also referred to as physiological parameter) of tracerkinetics, while the original SUV image presents radioactivityconcentrations. The at least one target image may be also referred to asa target parametric image. The dynamic parameter may be configured topresent the metabolism of a tracer injected into the sample. Exemplarydynamic parameters may include a perfusion rate of a tracer, a receptorbinding potential of the tracer, a distribution of the tracer in theplasma, a distribution of the tracer in the sample, a transport rate ofthe tracer from the plasma to a tissue (i.e., K1), a transport rate ofthe tracer from a tissue to the plasma (i.e., K2), or the like, or anycombination thereof.

In some embodiments, the at least one target image (i.e., targetparametric image) may be generated by inputting the image sequenceassociated with the subject into the target machine learning model. Thetarget parametric image may be an output of the target machine learningmodel. For example, the target machine learning model may determineand/or output the at least one target image based on the mappingrelationship between the specific image sequence associated with thespecific subject and the specific parametric image of the specificsubject. In some embodiments, the at least one target image may begenerated based on the image sequence and a corresponding plasma TAC ofthe subject. For example, the at least one target image may be generatedby inputting the image sequence and the corresponding plasma TACassociated with the subject into the target machine learning model. Thenthe target machine learning model may determine the at least one targetimage based on the mapping relationship between the specific imagesequence and the specific parametric image of the specific subject basedon the plasma TAC associated with the subject. In some embodiments, theplasma TAC associated with the subject may be determined based on theimage sequence. Detailed descriptions regarding the determination of theplasma TAC may be found elsewhere in the present disclosure (e.g., FIG.6 and the descriptions thereof).

It should be noted that the above description is merely provided for thepurposes of illustration, and not intended to limit the scope of thepresent disclosure. For persons having ordinary skills in the art,multiple variations or modifications may be made under the teachings ofthe present disclosure. However, those variations and modifications donot depart from the scope of the present disclosure. For example, inoperation 506, to generate the at least one target image with the inputof the image sequence, the target machine learning model may firstdetermine the corresponding plasma TAC based on the inputted imagesequence. Then the target machine learning model may determine the atleast one target image based on the corresponding plasma TAC and theimage sequence. In some embodiments, process 500 may further includeobtaining a plasma TAC of the subject.

FIG. 6 is a flowchart illustrating an exemplary process 600 forreconstructing an image according to some embodiments of the presentdisclosure. In some embodiments, one or more operations of process 600illustrated in FIG. 6 may be implemented in the imaging system 100illustrated in FIG. 1 . For example, process 600 illustrated in FIG. 6may be stored in the storage device 130 in the form of instructions, andinvoked and/or executed by the processing device 120 (e.g., theprocessor 210 of the computing device 200 as illustrated in FIG. 2 , theGPU 330 or CPU 340 of the mobile device 300 as illustrated in FIG. 3 ).

In 602, an image sequence associated with a subject may be obtained, theimage sequence including one or more images generated via scanning thesubject at one or more time periods (e.g., one or more consecutive timeperiods, one or more non-consecutive time periods). Operation 602 may beperformed by the acquisition module 402. The image sequence may besimilar to or same as that described in operation 502, and will not berepeated herein.

In 604, a plasma time activity curve (TAC) associated with the subjectmay be obtained. Operation 604 may be performed by the acquisitionmodule 402. As used herein, the plasma TAC may be also referred to as aplasma input function. The plasma TAC may be denoted by a function thatthe concentration of radioactivity of the tracer in the plasma changeswith time. The plasma TAC of the subject may be determined using a goldstandard technique, an arterialization of venous blood technique, a PETblood pool scan technique, a standard input function technique, afitting function technique, or the like, or a combination thereof. Usingthe golden standard technique, the arterial blood of the subject may besampled to measure plasma TAC of the subject. Using the arterializationof venous blood technique, the venous blood of the subject may besampled to measure plasma TAC of the subject. Using the PET blood poolscan technique, the plasma TAC of the subject may be determined based onthe image sequence. For example, the processing device 120 may determinea region of interest (ROI) (e.g., a region associated with the heart orarterial blood) from each of the one or more images in the imagesequence. The processing device 120 may identify a blood TAC from theone or more images based on the determined ROI and designate the bloodTAC as the plasma TAC. The plasma TAC identified from the image sequencemay be also referred to as an image-derived input function. Using thestandard input function technique, the plasma TAC of the subject may bedetermined based on a plurality of plasma TACs of multiple persons(e.g., patients) determined based on the golden standard technique.Further, the plurality of plasma TACs of multiple persons may benormalized and averaged to obtain the plasma TAC of the subject. Usingthe fitting function technique, the plasma TAC of the subject may bedetermined by fitting the plurality of plasma TACs of multiple persons.The plasma TAC of the subject determined based on the plurality ofplasma TACs of multiple persons may be also referred to as apopulation-based input function (or standard arterial input function,SAIF). In some embodiments, the plasma TAC of the subject may bedetermined based on the image sequence and the plurality of plasma TACsof multiple persons. The plasma TAC of the subject determined based onthe image-derived input function and the population-based input functionmay be also referred to as a population-based input function normalizedby image (also referred to as PBIFNI). For example, the plasma TAC maybe determined by normalizing the population-based input function usingthe image-derived input function. As a further example, the processingdevice 120 may average the population-based input function and theimage-derived input function to obtain the population-based inputfunction normalized by image.

In some embodiments, the plasma TAC may be determined based on the imagesequence using a trained machine learning model. The trained machinelearning model may be configured to provide a mapping between the imagesequence and the plasma TAC of the subject. The trained machine learningmodel may be used to determine the plasma TAC based on the mappingrelationship. For example, the image sequence may be inputted into thetrained machine learning model. The trained machine learning model maygenerate and output the plasma TAC. The trained machine learning modelmay be obtained from the model determination module 404, the storagedevice 130, or any other storage device. For example, the modeldetermination module 404 may generate the trained machine learning modelby training a machine learning model based on multiple groups oftraining data using a model training algorithm. Each group of themultiple groups of training data may include an image sequence and areference plasma TAC of a sample. The reference plasma TAC of a samplemay be determined according to one or more plasma TAC determinationtechniques as described above.

In 606, a target machine learning model may be obtained. Operation 606may be performed by the model determination module 404. The targetmachine learning model may be similar to or same as that described inoperation 504, and will not be repeated herein. For example, the targetmachine learning model may provide a mapping between a specific imagesequence and a specific target image presenting a dynamic parameterassociated with a specific subject (also referred to as a parametricimage). In other words, the target machine learning model may be used toconvert the specific image sequence associated with a specific subjectinto a specific parametric image. As another example, the target machinelearning model may provide a mapping between a specific image sequence,a specific plasma TAC, and a specific parametric image of a specificsubject. In some embodiments, the target machine learning model and thetrained machine learning model as described in operation 604 may beintegrated into one single model. In some embodiments, the targetmachine learning model and the trained machine learning model asdescribed in operation 604 may be separate and/or independent from eachother.

In 608, at least one target image may be generated by inputting theimage sequence and the plasma TAC associated with the subject into thetarget machine learning model. Operation 608 may be performed by theimage reconstruction module 406. The generation of the at least onetarget image by inputting the image sequence and the plasma TAC into thetarget machine learning model may be similar to or same as that inoperation 506, and will not be repeated herein.

It should be noted that the above description is merely provided for thepurposes of illustration, and not intended to limit the scope of thepresent disclosure. For persons having ordinary skills in the art,multiple variations or modifications may be made under the teachings ofthe present disclosure. However, those variations and modifications donot depart from the scope of the present disclosure. In someembodiments, process 600 may further include one or more storingoperations.

FIG. 7 is a flowchart illustrating an exemplary process 700 for traininga machine learning model according to some embodiments of the presentdisclosure. In some embodiments, one or more operations of process 700illustrated in FIG. 7 may be implemented in the imaging system 100illustrated in FIG. 1 . For example, process 700 illustrated in FIG. 7may be stored in the storage device 130 in the form of instructions, andinvoked and/or executed by the processing device 120 (e.g., theprocessor 210 of the computing device 200 as illustrated in FIG. 2 , theGPU 330 or CPU 340 of the mobile device 300 as illustrated in FIG. 3 ).In some embodiments, one portion of operation 506 illustrated in FIG. 5may be performed according to the process 700. For example, the targetmachine learning model as described in operation 506 may be determinedaccording to process 700.

In 702, multiple groups of training data may be obtained. The multiplegroups of training data may be associated with one or more samples.Operation 702 may be performed by the model determination module 404.The multiple groups of training data associated with one or more samplesmay form a training set. As used herein, a sample may be also referredto as a subject as described elsewhere in the present disclosure (e.g.,FIG. 1 and the descriptions thereof). For example, a sample may be theentire volume of a subject, or a portion of the subject, such as thehead, the thorax, the abdomen, or the like, or a combination thereof.For another example, a sample may be a specific organ, such as theheart, the esophagus, the trachea, the bronchus, the stomach, thegallbladder, the small intestine, the colon, the bladder, the ureter,the uterus, the fallopian tube, etc.

Each group of the multiple groups of training data may include an imagesequence and a reference parametric image corresponding to the imagesequence. An image sequence of a specific group may include dynamicactivity images (e.g., one or more SUV images) associated with one ofthe one or more samples. The dynamic activity images (e.g., one or moreSUV images) of the image sequence associated with a sample may beobtained from the scanner 110, the processing device 120, one or morestorage devices disclosed in the present disclosure (e.g., the storagedevice 130), etc. The one or more SUV images associated with the samplemay be reconstructed based on PET scan data (e.g., an original sinogram)collected during a PET scanning of the sample at one or more timeperiods (e.g., one or more consecutive time periods, one or morenon-consecutive time periods). In some embodiments, the originalsinogram may be four-dimensional (4D) data generated by processing rawdata (e.g., coincidence events). The reconstruction of the one or moreSUV images may be similar to or same as that of the image sequencedescribed in connection with operation 502, and will not be repeatedherein. For example, the one or more SUV images may be reconstructedusing a first image reconstruction algorithm. The first imagereconstruction algorithm may include an iterative algorithm, an analysisalgorithm, etc. The iterative algorithm may include a Maximum LikelihoodEstimation Method (MLEM) algorithm, an ordered subset expectationmaximization (OSEM), a 3D reconstruction algorithm, etc. The analysisalgorithm may include a filtered back projection (FBP) algorithm.

A reference parametric image of the specific group may present a dynamicparameter associated with the same sample as the image sequence of thespecific group. Each voxel or pixel of a reference parametric image mayrepresent a value of a physiological parameter (also referred to asdynamic parameter) of tracer kinetics as described elsewhere in thepresent disclosure (e.g., FIG. 5 and the descriptions thereof).

In some embodiments, a reference parametric image corresponding to theimage sequence may be reconstructed based on the PET scan data (e.g.,the original sinogram) using a second image reconstruction algorithm.The second image reconstruction algorithm may include a four-dimensional(4D) iteration technique. For example, the reference parametric imagemay be reconstructed based on the PET scan data (e.g., originalsinogram) using the MLEM algorithm. The processing device 120 mayreconstruct the reference parametric image according to Equation (2) asfollowing:

K ^(n+1) =K ^(n)1/PMPY/PK ^(n) M+S+RM  (2),

where K denotes a reference parametric image, Y denotes an originalsinogram, M denotes a relationship between a reference parametric imageand an image sequence, P denotes a projection matrix, S denotes ascatter sinogram, R denotes a random coincidences sinogram, and ndenotes the count (or number) of iterations using the four-dimensional(4D) iteration technique. The projection matrix may be set by a user oraccording to a default setting of the imaging system 100. The scattersinogram S and/or the random coincidence sinogram R may be determinedbased on original PET acquisitions (e.g., radiation events). Forexample, the scattering sinogram may be obtained by a scatter estimationapproach such as Monte Carlo scatter estimation technique. The randomcoincidence sinogram may be estimated by measuring delay events.

The relationship between the reference parametric image and the imagesequence M may satisfy Equation (3) as following:

KM=X  (3),

where X denotes the image sequence including one or more SUV images(also referred to as dynamic activity images). According to Equations(2) and (3), the reference parametric image may be reconstructed.

In some embodiments, the second reconstruction algorithm may include amaximum likelihood expectation maximization (MLEM) algorithm, anexpectation maximization (EM) algorithm, a parametric iterativecoordinate descent (PICD) algorithm, using a Patlak model, or the like,or any combination thereof.

In some embodiments, each group of the multiple groups of training datamay include a corresponding plasma TAC associated with one of the one ormore samples. More descriptions of the determination of the plasma TACmay be found elsewhere in the present disclosure (e.g., FIG. 6 and thedescriptions thereof).

In 704, a machine learning model may be obtained. Operation 704 may beperformed by the model determination module 404. In some embodiments,the machine learning model may be stored in a storage device as anapplication or a part thereof. The machine learning model may beconstructed based on at least one of a convolutional machine learningmodel (CNN), a fully convolutional neural network (FCN) model, agenerative adversarial network (GAN), a back propagation (BP) machinelearning model, a radial basis function (RBF) machine learning model, adeep belief nets (DBN) machine learning model, an Elman machine learningmodel, or the like, or a combination thereof. In some embodiments, themachine learning model may include multiple layers, for example, aninput layer, multiple hidden layers, and an output layer. The multiplehidden layers may include one or more convolutional layers, one or morepooling layers, one or more batch normalization layers, one or moreactivation layers, one or more fully connected layers, a cost functionlayer, etc. Each of the multiple layers may include a plurality ofnodes. The machine learning model may be trained to take dynamicactivity images (e.g., SUV images) as an input and one or moreparametric images as an output.

In some embodiments, the machine learning model may be defined by aplurality of architecture parameters and a plurality of learningparameters. The plurality of learning parameters may be altered duringthe training of the machine learning model using the multiple groups oftraining data, while the plurality of architecture parameters may not bealtered during the training of the machine learning model using themultiple groups of training data. The plurality of architectureparameters may be set and/or adjusted by a user before the training ofthe machine learning model. Exemplary architecture parameters of themachine learning model may include the size of a kernel of a layer, thetotal count (or number) of layers, the count (or number) of nodes ineach layer, a learning rate, a minibatch size, an epoch, etc. Exemplarylearning parameters of the machine learning model may include aconnected weight between two connected nodes, a bias vector relating toa node, etc. The connected weight between two connected nodes may beconfigured to represent a proportion of an output value of a node to beas an input value of another connected node. The bias vector relating toa node may be configured to control an output value of the nodedeviating from an origin.

In 706, the machine learning model may be trained using the multiplegroups of training data to generate a trained machine learning model.Operation 706 may be performed by the model determination module 404.Exemplary neural network training algorithms may include a gradientdescent algorithm, a Newton's algorithm, a Quasi-Newton algorithm, aLevenberg-Marquardt algorithm, a conjugate gradient algorithm, or thelike, or a combination thereof, as exemplified in FIG. 9 and thedescription thereof. In some embodiments, the machine learning model maybe trained by performing a plurality of iterations based on a costfunction. Before the plurality of iterations, the plurality of learningparameters of the machine learning model may be initialized. Forexample, the connected weights and/or the bias vector of nodes of themachine learning model may be initialized to be random values in arange, e.g., the range from −1 to 1. As another example, all theconnected weights of the machine learning model may have a same value inthe range from −1 to 1, for example, 0. As still an example, the biasvector of nodes in the machine learning model may be initialized to berandom values in a range from 0 to 1. In some embodiments, the pluralityof learning parameters of the machine learning model may be initializedbased on a Gaussian random algorithm, a Xavier algorithm, etc. Then theplurality of iterations may be performed to update the plurality oflearning parameters of the machine learning model until a condition issatisfied. The condition may provide an indication of whether themachine learning model is sufficiently trained. For example, thecondition may be satisfied if the value of the cost function associatedwith the machine learning model is minimal or smaller than a threshold(e.g., a constant). As another example, the condition may be satisfiedif the value of the cost function converges. The convergence may bedeemed to have occurred if the variation of the values of the costfunction in two or more consecutive iterations is smaller than athreshold (e.g., a constant). As still an example, the condition may besatisfied when a specified number of iterations are performed in thetraining process.

For each of the plurality of iterations, an image sequence (e.g.,dynamic activity images), a plasma TAC, and a reference parametric imagein one group of the multiple groups of training data may be inputtedinto the machine learning model. The image sequence, a plasma TAC, andthe reference parametric image may be processed by one or more layers ofthe machine learning model to generate at least one estimated parametricimage (e.g., a parametric image presenting a dynamic parameter)corresponding to the image sequence. The at least one estimatedparametric image may be compared with the reference parametric imagecorresponding to the image sequence based on the cost function of themachine learning model. The cost function of the machine learning modelmay be configured to assess a difference between an estimated value(e.g., the at least one estimated parametric image) of the machinelearning model and a desired value (e.g., the reference parametricimage). If the value of the cost function exceeds a threshold in acurrent iteration, the plurality of learning parameters of the machinelearning model may be adjusted and updated to cause the value of thecost function (i.e., the difference between the at least one estimatedparametric image and the reference parametric image) smaller than thethreshold. Accordingly, in a next iteration, another group of trainingdata may be inputted into the machine learning model to train themachine learning model as described above until the condition issatisfied. The trained machine learning model may be configured tooutput at least one estimated parametric image based on a mappingrelationship when the specific image sequence (e.g., dynamic activityimages) is inputted into the trained machine learning model. In someembodiments, the trained machine learning model may be determined basedon the updated plurality of learning parameters. In some embodiments,the trained machine learning model may be transmitted to the storagedevice 130, the storage module 408, or any other storage device forstorage.

In some embodiments, the training set of the target machine learningmodel may be updated based on added data (e.g., the image sequenceobtained in 502 and the parametric image generated in 506) over a periodof time (e.g., every other month, every two months, etc.). In someembodiments, the target machine learning model may be updated accordingto an instruction of a user, clinical demands, the updated training set,or a default setting of the imaging system 100. For example, the targetmachine learning model may be updated at set intervals (e.g., everyother month, every two months, etc.). As another example, the targetmachine learning model may be updated based on added data in thetraining set of the target machine learning model over a period of time(e.g., every other month, every two months, etc.). If the quantity ofthe added data in the training set over a period of time is greater thana threshold, the target machine learning model may be updated based onthe updated training set.

In 708, multiple groups of validation data may be obtained. The multiplegroups of validation data may include data that is not included in thetraining set. Operation 708 may be performed by the model determinationmodule 404. The multiple groups of validation data may form a validationset. Each group of the multiple groups of validation data may include animage sequence (e.g., dynamic activity images) as an input of thetrained machine learning model and at least one reference parametricimage corresponding to a same object. As used herein, an object may bealso referred to as a subject as described elsewhere in the presentdisclosure (e.g., FIG. 1 and the descriptions thereof). An imagesequence of a specific group may include one or more SUV imagesassociated with a specific object. A reference parametric image of thespecific group of validation data may present a dynamic parameterassociated with the same specific object as the image sequence of thespecific group of validation data. The SUV images of an image sequencein the validation set may be obtained in a similar to or same way as theSUV images in an image sequence in the training set. A referenceparametric image in the validation set may be obtained in a similar toor same way as the reference parametric image in the training set. Thedetermination of the image sequence and the reference parametric imagein the validation set may be similar to or same as that described inoperation 702, and will not be repeated herein. In some embodiments,each group of the multiple groups of validation data may include acorresponding plasma TAC associated with one of the one or more objects.More descriptions of the determination of the plasma TAC may be foundelsewhere in the present disclosure (e.g., FIG. 6 and the descriptionsthereof).

In some embodiments, the multiple groups of validation data and themultiple groups of training data may belong to a same data set. The dataset may include multiple image sequences and multiple correspondingparametric images, wherein each of the multiple image sequences includesone or more SUV images. For example, 70% of the data set may be themultiple groups of training data, and 20% of the data set may be themultiple groups of validation data.

In 710, a target machine learning model may be determined by adjustingthe trained machine learning model using the multiple groups ofvalidation data. Operation 710 may be performed by the modeldetermination module 404. The trained machine learning model may beadjusted and/or optimized based on the status of the trained machinelearning model (e.g., underfitting, overfitting). The trained machinelearning model may be adjusted by adjusting the plurality ofarchitecture parameters based on the validation set if the trainedmachine learning model is underfitting or overfitting; otherwise, thetrained machine learning model determined in operation 706 may bedesignated as the target machine learning model.

In response to determining that the trained machine learning model isunderfitting, multiples operations, such as increasing the complexity ofthe machine learning model (e.g., by increasing the number of layers,increasing the size of a convolutional kernel, increasing the number ofnodes in each layer), and decreasing the learning rate, may be adopted.In response to determining that the trained machine learning model isoverfitting, multiples operations, such as decreasing the complexity ofthe machine learning model (e.g., by decreasing the number of layers,decreasing the number of the size of a convolutional kernel, decreasingthe number of layers, decreasing the number of nodes in each layer),decreasing the learning rate, and decreasing the value of the epoch, maybe adopted.

The status of the trained machine learning model may be determined basedon an accuracy over the validation set and/or an accuracy over thetraining set. As used herein, the accuracy of the trained machinelearning model may be defined by a similarity between an estimated value(e.g., an estimated parametric image) and a desired value (e.g., areference parametric image in a group of validation data or trainingdata). For example, an image sequence and a plasma TAC in a specificgroup of validation data may be inputted into the trained machinelearning model. The trained machine learning model may generate and/oroutputted an estimated parametric image based on the inputted imagesequence and the plasma TAC. The similarity between the estimatedparametric image and a reference validation image in the specific groupof validation data may be determined. The greater the similarity is, thehigher the accuracy of the trained machine learning model may be. Thetrained machine learning model may be overfitting if the accuracy overthe validation set is lower than the accuracy over the training set. Forexample, when the accuracy over the training set increases, but theaccuracy over the validation set stays the same or decreases, it may bedetermined that the trained machine learning model is overfitting. Thetrained machine learning model may be underfitting if the accuracy overthe validation set is higher than the accuracy over the training set.

In some embodiments, if the accuracy of the trained machine learningmodel determined based on the validation set exceeds a threshold, thetrained machine learning model may be determined as the target machinelearning model. If the accuracy of the trained machine learning modeldetermined based on the validation set is small than the threshold, thetrained machine learning model may be adjusted to increase the accuracyof the trained machine learning model.

In some embodiments, after the trained machine learning mod& isadjusted, the adjusted trained machine learning model may be furthertrained by the training set as described in operation 706. The targetmachine learning model may be determined unless the newly trainedmachine learning model is either overfitting nor underfitting, using anewly validation set. In some embodiments, the target machine learningmodel may be transmitted to the storage device 130, the storage module408, or any other storage device for storage.

It should be noted that the above description is merely provided for thepurposes of illustration, and not intended to limit the scope of thepresent disclosure. For persons having ordinary skills in the art,multiple variations or modifications may be made under the teachings ofthe present disclosure. However, those variations and modifications donot depart from the scope of the present disclosure. In someembodiments, the corresponding plasma TACs may be not inputted into themachine learning model along with the image sequence. In someembodiments, before generating the at least one estimated parametricimage, a plasma TAC corresponding to the image sequence may bedetermined as described elsewhere in the present disclosure. Thecorresponding plasma TAC, along with the image sequence, may beprocessed by the machine learning model to generate the at least oneestimated parametric image.

FIG. 8 is a flowchart illustrating an exemplary process 800 for traininga machine learning model according to some embodiments of the presentdisclosure. In some embodiments, one or more operations of process 800illustrated in FIG. 8 may be implemented in the imaging system 100illustrated in FIG. 1 . For example, process 800 illustrated in FIG. 8may be stored in the storage device 130 in the form of instructions, andinvoked and/or executed by the processing device 120 (e.g., theprocessor 210 of the computing device 200 as illustrated in FIG. 2 , theGPU 330 or CPU 340 of the mobile device 300 as illustrated in FIG. 3 ).In some embodiments, one portion of operation 506 illustrated in FIG. 5may be performed according to the process 700. For example, the targetmachine learning model as described in operation 506 may be determinedaccording to process 800. In some embodiments, one portion of operation608 illustrated in FIG. 6 may be performed according to the process 800.For example, the target machine learning model as described in operation608 may be determined according to process 800. In some embodiments,operation 706 as illustrated in FIG. 7 may be performed according toprocess 800.

In 802, a machine learning model including one or more parameters may beinitialized. Operation 802 may be performed by the model determinationmodule 404. The machine learning model may be obtained as described inconnection with operation 704.

In some embodiments, the one or more parameters of the machine learningmodel may include a plurality of architecture parameters and a pluralityof learning parameters. Exemplary architecture parameters of the machinelearning model may include the size of a convolutional kernel, thenumber of layers, the number of nodes in each layer, a learning rate, aminibatch size, an epoch, etc. Exemplary learning parameters of themachine learning model may include a connected weight between twoconnected nodes, a bias vector relating to a node, etc. The connectedweight between two connected nodes may be configured to represent aproportion of an output value of a node to be as an input value ofanother connected node. In some embodiments, the connected weights ofthe machine learning model may be initialized to be random values in arange, e.g., the range from −1 to 1. In some embodiments, all theconnected weights of the machine learning model may have a same value inthe range from −1 to 1, for example, 0. The bias vector relating to anode may be configured to control an output value of the node deviatingfrom an origin. In some embodiments, the bias vector of nodes in themachine learning model may be initialized to be random values in a rangefrom 0 to 1. In some embodiments, the parameters of the machine learningmodel may be initialized based on a Gaussian random algorithm, a Xavieralgorithm, etc.

In 804, an image sequence and a corresponding plasma TAC may be inputtedinto the machine learning model. Operation 804 may be performed by themodel determination module 404. The image sequence and the correspondingplasma TAC may be obtained as described in connection with operation702. For example, the image sequence may include one or more dynamicactivity images, such as SUV images imaging a sample as describedelsewhere in the present disclosure (e.g., FIG. 7 and the descriptionsthereof). As another example, the corresponding plasma TAC may bedetermined based on the image sequence. The machine learning model maybe obtained as described in connection with operation 704. Moredescriptions of the machine learning model may be found elsewhere in thepresent disclosure (e.g., FIGS. 5-7 and the descriptions thereof).

After inputting the image sequence and the corresponding plasma TAC intothe machine learning model, the image sequence and the correspondingplasma TAC may be processed by multiple layers of the machine learningmodel to generate at least one portion of an estimated parametric image.During the training process, one or more first features may be extractedfrom the at least one portion of the estimated parametric image. The oneor more first features may be related to values of one or more pixels orvoxels of the at least one portion of the estimated parametric image. Insome embodiments, the one or more first features may be extracted fromthe at least one portion of the estimated parametric image by themachine learning model (e.g., a convolution layer of the machinelearning model). The one or more first features may include a low-levelfeature (e.g., an edge feature, a texture feature, etc.), a high-levelfeature (e.g., a semantic feature), or a complicated feature (e.g., adeep hierarchical feature) that is determined by the machine learningmodel.

In 806, a reference parametric image corresponding to the image sequencemay be inputted into the machine learning model. Operation 806 may beperformed by the model determination module 404. The referenceparametric image may be obtained as described in connection withoperation 706. For example, the reference parametric image may also bereferred to as a parametric image, presenting a dynamic parameterassociated with the same sample as the image sequence. The referenceparametric image may be reconstructed using a four-dimensional (4D)iteration technique.

During the training process, one or more second features of thereference parametric image may be extracted from at least one portion ofthe reference parametric image. Each of the one or more second featuresmay correspond to one of the one or more first features. As used herein,a second feature of a reference parametric image corresponding to afirst feature of at least one portion of the estimated parametric imagemay refer to that the pixels or the voxels corresponding to the secondfeature and the pixels or the voxels corresponding to the first featuremay be at the same position in the at least one portion of the estimatedparametric image and the at least one portion of the referenceparametric image, respectively. The second feature may include alow-level feature (e.g., an edge feature, a texture feature, etc.), ahigh-level feature (e.g., a semantic feature), a complicated feature(e.g., a deep hierarchical feature), etc., as described above.

In 808, a value of a cost function (also referred to as a loss function)may be determined based on the image sequence and the referenceparametric image. Operation 808 may be performed by the modeldetermination module 404. The cost function may be configured to assessa difference between an estimated value (e.g., at least one estimatedparametric image) of the machine learning model and a desired value(e.g., the reference parametric image). For example, the cost functionmay be determined based on the one or more first features and the one ormore second features. In some embodiments, the image sequence may beinputted to the machine learning model via an input layer (e.g., theinput layer 920 as illustrated in FIG. 9 ), and then be transferred froma first hidden layer of the machine learning model (e.g., theconvolution layers 940-1 as illustrated in FIG. 9 ) to the last hiddenlayer of the machine learning model. The image sequence may be processedin at least a portion of the multiple hidden layers to generate the atleast one estimated parametric image. For example, the inputted imagesequence may be processed by one or more convolution layer (e.g., theconvolution layers 940-1 as illustrated in FIG. 9 ). The one or moreconvolution layers may be configured to perform an image transformationoperation, an image enhancement operation, an image denoising operation,or any other operations on the image sequence based on the parametersrelating to nodes in the one or more convolution layers. The at leastone estimated parametric image processed by the hidden layers before thecost function layer may be inputted to the cost function layer. Thevalue of the cost function layer may be determined based on the one ormore first features and the one or more second features generated by thelayers before the cost function layers via processing the at least oneestimated parametric and the reference parametric image, respectively.

In 810, a determination may be made as to whether a first condition issatisfied. Operation 810 may be performed by the model determinationmodule 404. If the first condition is satisfied, process 800 may proceedto operation 814. If the first condition is not satisfied, process 800may proceed to 812. The first condition may provide an indicationwhether the machine learning model is sufficiently trained. In someembodiments, the first condition may relate to a value of the costfunction. For example, the first condition may be satisfied if the valueof the cost function is minimal or smaller than a threshold (e.g., aconstant). As another example, the first condition may be satisfied ifthe value of the cost function converges. In some embodiments,convergence may be deemed to have occurred if the variation of thevalues of the cost function in two or more consecutive iterations isequal to or smaller than a threshold (e.g., a constant). In someembodiments, convergence may be deemed to have occurred if a differencebetween the value of the cost function and a target value is equal to orsmaller than a threshold (e.g., a constant). In some embodiments, thefirst condition may be satisfied when a specified number of iterationsrelating to the first feature and the second feature are performed inthe training process.

In 812, the one or more parameters of the machine learning model may beupdated. Operation 812 may be performed by the model determinationmodule 404. In some embodiments, at least one of the plurality oflearning parameters may be adjusted. For example, the parameter value ofat least some nodes may be adjusted until the value of the cost functionrelating satisfy the first condition. In some embodiments, the pluralityof learning parameters of the machine learning model may be adjustedbased on a back-propagation (BP) algorithm. Exemplary BP algorithms mayinclude a stochastic gradient descent algorithm, an Adam algorithm, anAdagrad algorithm, an Adadelta algorithm, an RMSprop algorithm, or thelike, or a combination thereof.

In 814, a determination may be made as to whether a second condition issatisfied. Operation 814 may be performed by the model determinationmodule 404. If the second condition is satisfied, process 800 mayproceed to 816. If the second condition is not satisfied, process 800may return to 804 in which another image sequence may be extracted froma training set. The second condition may provide an indication whetherthe training may be terminated. In some embodiments, the secondcondition may be satisfied if a specified number of the image sequencesand the reference parametric images are processed by the machinelearning model or a specific count of iterations are performed.

In 816, a trained machine learning model may be determined. Operation816 may be performed by the model determination module 404. In someembodiments, the trained machine learning model may be determined basedon the updated parameters.

In some embodiments, process 800 may be repeated with respect tomultiple training data including different groups of image sequences,plasma TACs, and the reference parametric images to improve or optimizethe machine learning model until a termination condition is satisfied.In different rounds of process 800, different groups of image sequencesand the reference parametric images may be inputted into the machinelearning model. In some embodiments, the termination condition may bethat a specific number of groups of image sequences and the referenceparametric images have been analyzed. In some embodiments, thetermination condition may be that a specific number of iterations havebeen performed.

It should be noted that the above description is merely provided for thepurposes of illustration, and not intended to limit the scope of thepresent disclosure. For persons having ordinary skills in the art,multiple variations or modifications may be made under the teachings ofthe present disclosure. However, those variations and modifications donot depart from the scope of the present disclosure. In someembodiments, operations 804 and 806 may be omitted.

FIG. 9 is a schematic diagram illustrating an exemplary convolutionalneural network (CNN) model 900 according to some embodiments of thepresent disclosure.

The CNN model may include an input layer 920, hidden layers 940, and anoutput layer 960. The multiple hidden layers 940 may include one or moreconvolutional layers, one or more Rectified Linear Units layers (ReLUlayers), one or more pooling layers, one or more fully connected layers,or the like, or a combination thereof.

For illustration purposes, exemplary hidden layers 940 of the CNN model,including a convolutional layer 940-1, a pooling layer 940-2, and afully connected layer 940-N, are illustrated. As described in connectionwith process 800, the model determination module 404 may acquire animage sequence and a plasma TAC as an input of the CNN model. The imagesequence may be expressed as a 4D matrix including a plurality ofelements (e.g., pixels or voxels). Each of the plurality of elements inthe matrix may have a value (also referred to as pixel/voxel value)representing a characteristic of the element.

The convolutional layer 940-1 may include a plurality of kernels (e.g.,A, B, C, and D). For example, the number of the plurality of kernels maybe in a range from 16 to 64, for example, 32. The plurality of kernelsmay be used to extract features of a training sample (e.g., the imagesequence, the plasma TAC, and the reference parametric image asdescribed in FIG. 8 ). In some embodiments, each of the plurality ofkernels may filter a portion (e.g., a region) of the image sequence toproduce a specific feature corresponding to the portion of the imagesequence. The feature may include a low-level feature (e.g., an edgefeature, a texture feature, etc.), a high-level feature (e.g., asemantic feature), or a complicated feature (e.g., a deep hierarchicalfeature) that is calculated based on the kernel(s).

The pooling layer 940-2 may take the output of the convolutional layer940-1 as an input. The pooling layer 940-2 may include a plurality ofpooling nodes (e.g., E, F, G, and H). The plurality of pooling nodes maybe used to sample the output of the convolutional layer 940-1, and thusmay reduce the computational load of data processing and increase thespeed of data processing of the imaging system 100. In some embodiments,the model determination module 404 may reduce the volume of the matrixcorresponding to the image sequence in the pooling layer 940-2.

The fully connected layer 940-N may include a plurality of neurons(e.g., 0, P, M, and N). The plurality of neurons may be connected to aplurality of nodes from the previous layer, such as a pooling layer. Inthe fully connected layer 940-N, the model determination module 404 maydetermine a plurality of vectors corresponding to the plurality ofneurons based on the features of the training samples (e.g., the imagesequences, the plasma TACs and the reference parametric image asdescribed in FIG. 8 ) and further weigh the plurality of vectors with aplurality of weighting coefficients (i.e., connected weight).

In the output layer 960, the model determination module 404 maydetermine an output, such as a target image (e.g., parametric images),based on the plurality of vectors and weighting coefficients obtained inthe fully connected layer 940-N.

It shall be noted that the CNN model may be modified when applied indifferent conditions. For example, in a training process, a lossfunction (also referred to as cost function in the disclosure) layer maybe added to specify the deviation between an estimated output (e.g., atleast one estimated parametric image) and a true label (e.g., areference parametric image corresponding to the image sequence).

In some embodiments, the model determination module 404 may get accessto multiple processing units, such as GPUs, in the imaging system 100.The multiple processing units may perform parallel processing in somelayers of the CNN model. The parallel processing may be performed insuch a manner that the calculations of different nodes in a layer of theCNN model may be assigned to two or more processing units. For example,one GPU may run the calculations corresponding to kernels A and B, andthe other GPU(s) may run the calculations corresponding to kernels C andD in the convolutional layer 940-1. Similarly, the calculationscorresponding to different nodes in other type of layers in the CNNmodel may be performed in parallel by the multiple GPUs.

EXAMPLE

The examples are provided for illustration purposes, and not intended tolimit the scope of the present disclosure.

Example 1 Exemplary PET Torsos Images of Patients Reconstructed Using aLinear Patlak Model

FIG. 10 shows exemplary torsos images of three patients reconstructedaccording to some embodiments of the present disclosure. As shown inFIG. 10 , Image 1-6 are parametric images reconstructed based on SUVimages using a linear Patlak model. The SUV images may be reconstructedusing a 3D iterative algorithm (e.g., the MLEM algorithm, the OSEMalgorithm). Image 1 and Image 2 are a coronal view and a sagittal viewof the torso of patient A, respectively. Image 3 and Image 4 are acoronal view and a sagittal view of the torso of patient B,respectively. Image 5 and Image 6 are a coronal view and a sagittal viewof the torso of patient C, respectively.

Example 2 Exemplary PET Torsos Images of Three Patients ReconstructedUsing a 4D Iteration Technique

FIG. 11 shows exemplary images of the torsos of three patients describedin FIG. 10 reconstructed according to some embodiments of the presentdisclosure. As shown in FIG. 11 , Image 1′-6′ are parametric imagesreconstructed using a 4D iterative technique as described in operation702. Image 1′-6′ correspond to Image 1-6 as described in FIG. 10 ,respectively.

Example 3 Exemplary PET Torsos Images of Three Patients ReconstructedUsing a Target Machine Learning Model

FIG. 12 shows exemplary torsos images of three patients described inFIG. 10 reconstructed according to some embodiments of the presentdisclosure. As shown in FIG. 12 , Image 1″-6″ are parametric imagesreconstructed using a target machine learning model according to process500 and/or 600. Image 1″-6″ correspond to Image 1-6 as described in FIG.10 and Image 1′-6′ as described in FIG. 11 , respectively.

As shown in FIG. 10 , FIG. 11 and/or FIG. 12 , Image 1″-6″ reconstructedusing the target machine learning model in FIG. 12 are more similar orclose to corresponding Image 1′-6′, respectively, reconstructed usingthe 4D iteration technique in FIG. 11 than corresponding Image 1-6,respectively, reconstructed using the linear Patlak model in FIG. 10 .As used herein, Image 1″ are more similar or close to Image 1′ thanImage 1 may refer to that a similarity between the Image 1′ and Image 1″are greater than a similarity between the Image 1′ and Image 1.

Having thus described the basic concepts, it may be rather apparent tothose skilled in the art after reading this detailed disclosure that theforegoing detailed disclosure is intended to be presented by way ofexample only and is not limiting. Various alterations, improvements, andmodifications may occur and are intended to those skilled in the art,though not expressly stated herein. These alterations, improvements, andmodifications are intended to be suggested by this disclosure, and arewithin the spirit and scope of the exemplary embodiments of thisdisclosure.

Moreover, certain terminology has been used to describe embodiments ofthe present disclosure. For example, the terms “one embodiment,” “anembodiment,” and/or “some embodiments” mean that a particular feature,structure or characteristic described in connection with the embodimentis included in at least one embodiment of the present disclosure.Therefore, it is emphasized and should be appreciated that two or morereferences to “an embodiment” or “one embodiment” or “an alternativeembodiment” in various portions of this specification are notnecessarily all referring to the same embodiment. Furthermore, theparticular features, structures or characteristics may be combined assuitable in one or more embodiments of the present disclosure.

Further, it will be appreciated by one skilled in the art, aspects ofthe present disclosure may be illustrated and described herein in any ofa number of patentable classes or context including any new and usefulprocess, machine, manufacture, or composition of matter, or any new anduseful improvement thereof. Accordingly, aspects of the presentdisclosure may be implemented entirely hardware, entirely software(including firmware, resident software, micro-code, etc.) or combiningsoftware and hardware implementation that may all generally be referredto herein as a “unit,” “module,” or “system.” Furthermore, aspects ofthe present disclosure may take the form of a computer program productembodied in one or more computer-readable media having computer readableprogram code embodied thereon.

A computer readable signal medium may include a propagated data signalwith computer readable program code embodied therein, for example, inbaseband or as part of a carrier wave. Such a propagated signal may takeany of a variety of forms, including electromagnetic, optical, or thelike, or any suitable combination thereof. A computer readable signalmedium may be any computer readable medium that is not a computerreadable storage medium and that may communicate, propagate, ortransport a program for use by or in connection with an instructionexecution system, apparatus, or device. Program code embodied on acomputer readable signal medium may be transmitted using any appropriatemedium, including wireless, wireline, optical fiber cable, RF, or thelike, or any suitable combination of the foregoing.

Computer program code for carrying out operations for aspects of thepresent disclosure may be written in any combination of one or moreprogramming languages, including an object-oriented programming languagesuch as Java, Scala, Smalltalk, Eiffel, JADE, Emerald, C++, C #, VB.NET, Python or the like, conventional procedural programming languages,such as the “C” programming language, Visual Basic, Fortran 2103, Perl,COBOL 2102, PHP, ABAP, dynamic programming languages such as Python,Ruby, and Groovy, or other programming languages. The program code mayexecute entirely on the user's computer, partly on the user's computer,as a stand-alone software package, partly on the user's computer andpartly on a remote computer or entirely on the remote computer orserver. In the latter scenario, the remote computer may be connected tothe user's computer through any type of network, including a local areanetwork (LAN) or a wide area network (WAN), or the connection may bemade to an external computer (for example, through the Internet using anInternet Service Provider) or in a cloud computing environment oroffered as a service such as a Software as a Service (SaaS).

Furthermore, the recited order of processing elements or sequences, orthe use of numbers, letters, or other designations, therefore, is notintended to limit the claimed processes and methods to any order exceptas may be specified in the claims. Although the above disclosurediscusses through various examples what is currently considered to be avariety of useful embodiments of the disclosure, it is to be understoodthat such detail is solely for that purpose, and that the appendedclaims are not limited to the disclosed embodiments, but, on thecontrary, are intended to cover modifications and equivalentarrangements that are within the spirit and scope of the disclosedembodiments. For example, although the implementation of variouscomponents described above may be embodied in a hardware device, it mayalso be implemented as a software-only solution, for example, aninstallation on an existing server or mobile device.

Similarly, it should be appreciated that in the foregoing description ofembodiments of the present disclosure, various features are sometimesgrouped together in a single embodiment, figure, or description thereoffor the purpose of streamlining the disclosure aiding in theunderstanding of one or more of the various inventive embodiments. Thismethod of disclosure, however, is not to be interpreted as reflecting anintention that the claimed subject matter requires more features thanare expressly recited in each claim. Rather, inventive embodiments liein less than all features of a single foregoing disclosed embodiment.

In some embodiments, the numbers expressing quantities or propertiesused to describe and claim certain embodiments of the application are tobe understood as being modified in some instances by the term “about,”“approximate,” or “substantially.” For example, “about,” “approximate,”or “substantially” may indicate ±20% variation of the value itdescribes, unless otherwise stated. Accordingly, in some embodiments,the numerical parameters set forth in the written description andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by a particular embodiment. Insome embodiments, the numerical parameters should be construed in lightof the number of reported significant digits and by applying ordinaryrounding techniques. Notwithstanding that the numerical ranges andparameters setting forth the broad scope of some embodiments of theapplication are approximations, the numerical values set forth in thespecific examples are reported as precisely as practicable.

Each of the patents, patent applications, publications of patentapplications, and other material, such as articles, books,specifications, publications, documents, things, and/or the like,referenced herein is hereby incorporated herein by this reference in itsentirety for all purposes, excepting any prosecution file historyassociated with same, any of same that is inconsistent with or inconflict with the present document, or any of same that may have alimiting affect as to the broadest scope of the claims now or laterassociated with the present document. By way of example, should there beany inconsistency or conflict between the description, definition,and/or the use of a term associated with any of the incorporatedmaterial and that associated with the present document, the description,definition, and/or the use of the term in the present document shallprevail.

In closing, it is to be understood that the embodiments of theapplication disclosed herein are illustrative of the principles of theembodiments of the application. Other modifications that may be employedmay be within the scope of the application. Thus, by way of example, butnot of limitation, alternative configurations of the embodiments of theapplication may be utilized in accordance with the teachings herein.Accordingly, embodiments of the present application are not limited tothat precisely as shown and described.

What is claimed is:
 1. A system for image reconstruction, comprising: atleast one storage device storing executable instructions, and at leastone processor in communication with the at least one storage device,when executing the executable instructions, causing the system to:obtain an image sequence associated with a subject, the image sequenceincluding one or more images generated via scanning the subject at oneor more time periods; obtain a plasma time activity curve associatedwith the subject; obtain a target machine learning model; and generate,based on the image sequence and the plasma time activity curve, at leastone target image using the target machine learning model.
 2. The systemof claim 1, wherein the one or more time periods are non-consecutive. 3.The system of claim 1, wherein the at least one target image presents adynamic parameter associated with the subject.
 4. The system of claim 1,wherein to generate, based on the image sequence and the plasma timeactivity curve, the at least one target image using the target machinelearning model, the at least one processor is further configured todirect the system to: input the image sequence associated with thesubject and the plasma time activity curve into the target machinelearning model; and convert the image sequence into the at least onetarget image.
 5. The system of claim 1, wherein to obtain the plasmatime activity curve associated with the subject, the at least oneprocessor is further configured to direct the system to: obtain, basedon the image sequence, the plasma time activity curve associated withthe subject using an additional target machine learning model, whereinthe additional target machine learning model provides a mapping betweenthe image sequence and the plasma time activity curve.
 6. The system ofclaim 1, wherein to obtain the plasma time activity curve associatedwith the subject, the at least one processor is further configured todirect the system to: obtain, based on the image sequence, the plasmatime activity curve associated with the subject using the target machinelearning model.
 7. The system of claim 1, wherein the target machinelearning model is obtained by: obtaining multiple groups of trainingdata associated with one or more samples, each group of the multiplegroups of training data including a first image sequence and a firstparametric image corresponding to the first image sequence, the firstparametric image presenting dynamic parameter associated with one of theone or more samples; and generating the target machine learning model bytraining a machine learning model using the multiple groups of trainingdata.
 8. The system of claim 7, wherein the obtaining multiple groups oftraining data associated one or more samples includes: for each group ofthe multiple groups of training data, obtaining projection dataassociated with the one of the one or more samples; generating, based onthe projection data, the first image sequence using a first imagereconstruction algorithm; and generating, based on the projection data,the first parametric image using a second image reconstructionalgorithm.
 9. The system of claim 8, wherein the first imagereconstruction algorithm includes at least one of a Maximum LikelihoodEstimation Method (MLEM) algorithm, an ordered subset expectationmaximization (OSEM) algorithm, a three-dimensional (3D) reconstructionalgorithm, or a filtered back projection (FBP) algorithm.
 10. The systemof claim 8, wherein the second image reconstruction algorithm includes afour-dimensional (4D) iteration technique.
 11. The system of claim 7,wherein the target machine learning model is further obtained by:obtaining a reference plasma time activity curve associated with the oneof the one or more samples, wherein the generating the target machinelearning model by training the machine learning model using the multiplegroups of training data includes: training, based on the referenceplasma time activity curve, the machine learning model using themultiple groups of training data.
 12. The system of claim 11, whereinthe reference plasma time activity curve associated with the one of theone or more samples is determined based on the training image sequenceassociated with the one of the one or more samples.
 13. The system ofclaim 7, wherein the target machine learning model is further obtainedby: obtaining multiple groups of validation data, each group of themultiple groups of validation data including a second image sequence anda second parametric image corresponding to the second image sequence,the second parametric image presenting dynamic parameter associated withthe group of validation data; and adjusting the target machine learningmodel using the multiple groups of validation data.
 14. The system ofclaim 1, wherein the target machine learning model is constructed basedon a deep learning neural network model.
 15. The system of claim 14,wherein the deep learning neural network model includes a convolutionneural network (CNN) model.
 16. A method for image reconstructionimplemented on a computing apparatus, the computing apparatus includingat least one processor and at least one storage device, the methodcomprising: obtaining an image sequence associated with a subject, theimage sequence including one or more images generated via scanning thesubject at one or more time periods; obtaining a plasma time activitycurve associated with the subject; obtaining a target machine learningmodel; and generating, based on the image sequence and the plasma timeactivity curve, at least one target image using the target machinelearning model.
 17. The method of claim 16, wherein the one or more timeperiods are non-consecutive.
 18. The method of claim 16, whereingenerating, based on the image sequence and the plasma time activitycurve, the at least one target image using target machine learning modelfurther includes: inputting the image sequence associated with thesubject and the plasma time activity curve into the target machinelearning model; and converting the image sequence into the at least onetarget image.
 19. The method of claim 16, wherein the obtaining thetarget machine learning model includes: obtaining multiple groups oftraining data associated one or more samples, each group of the multiplegroups of training data including a first image sequence and a firstparametric image corresponding to the image sequence, the firstparametric image presenting the dynamic parameter associated with one ofthe one or more samples; and generating the target machine learningmodel by training a machine learning model using the multiple groups oftraining data.
 20. A non-transitory computer-readable medium storing atleast one set of instructions, wherein when executed by at least oneprocessor, the at least one set of instructions directs the at least oneprocessor to perform acts of: obtaining an image sequence associatedwith a subject, the image sequence including one or more imagesgenerated via scanning the subject at one or more time periods;obtaining a plasma time activity curve associated with the subject;obtaining a target machine learning model; and generating, based on theimage sequence and the plasma time activity curve, at least one targetimage using the target machine learning model.